This invention related to the field of bar codes and, in particular, to a small, reliable manual bar code scanner that can be embedded in other electronic devices, for example, a mobile telephone.
Bar codes have become ubiquitous in today""s society. Nearly every product sold bears a bar code which identifies the type of product, the manufacturer of the product and the identity of the product. In the very near future, it is envisioned that bar code readers will be coupled with mobile telephones to allow users of the device to scan and transmit numbers over the phone which have been scanned from a bar code. One application of this technology is to allow consumers to place orders for products from printed advertisements in which bar codes may be used to input information necessary to complete the sale of the item, for example, the seller""s telephone number and the bar code of the item being purchased. It may also be possible to scan the buyer""s credit card information directly from the credit card being used to complete the transaction, provided the credit card bears the buyer""s account number in bar code format.
Currently, there are two types of non-contact bar code scanners available in the market place. These are bar code readers that can scan a bar code without the reader physically contacting the bar code. One is an area scan bar code reader that uses a CMOS camera sensor. The other type is a one dimensional laser scanner, which is typically used at a cash register. It shows one red horizontal line and uses oscillating mirrors to scan. These types of bar code readers are very reliable, because they automatically scan over same bar code many times to reduce errors, typically, about 30 times per second. In other words, it integrates the signal to improve the signal-to-noise ratio. This is the key advantage of this type of scanner. However, the drawback with these types of scanners is that they are relatively large to include the scanning mirror or too expensive due to the requirement for the camera type CMOS sensor. As such, they are not suitable for embedded, portable applications, such as the one described above.
There are also bar code readers which are less expensive which are based on a manual scan. These are one-pass scanners and require physical contact between the scanner and the bar code. These types of scanners, while inexpensive and portable, are also very unreliable and error prone, often requiring that a user scan many times to get an error free reading of the bar code. A light pen type bar code reader is one example of such a device.
It is therefore desirable to provide a bar code scanner that is small, portable and inexpensive, such that portable, embedded applications are possible, while still retaining the reliability of the larger, more expensive units.
The present invention overcomes the deficiencies in the art by providing a manual bar code scanner that scans the bar code multiple times in one pass. This is accomplished by providing three sensors adjacent to each other such that, as the scanner is scanned over the bar code, the bar code is read three times.
Specifically, the invention consists of a bar code scanner having preferably three light sensors with corresponding light sources for illuminating the bar code. In the preferred embodiment, the sensor diodes are spaced side-by-side approximately 2 mm apart. The same bar code is thus read by all three sensors in series as the bar code is manually scanned one time. Errors in the reading of the bar code are eliminated by a bit-wise majority voting scheme, which is able to correct a one-time read error in any single bit.
Three light sources which act as source of reflected light for their corresponding sensors are modulated at 100 kHz. This has an effect similar to a chopper circuit. Thus, reflected light sensed at the sensors is much higher frequency than the bar code signal itself. As a result, the reflected light signal at the sensor can be easily amplified and demodulated as a high frequency AC signal. Also, interference light such as florescent light will not interfere with reflected light signal, because reflected signal will be band pass filtered to filter out any interfering signals. In the preferred embodiment, the bar code signal is typically a relatively low frequency ( less than 3 Khz) signal when the user manually scans over it. The light source operates as a modulator to generate a high frequency (about 100 kHz) AC signal for ease of signal processing in the receiver.
Thus, the novel aspects of the present invention are the modulation of the light sources at a high frequency and synchronous demodulation, bit-wise majority vote to correct read errors and the side-by-side placement of the light source/light sensor pairs to enable multiple reads per pass.